C# KB: C# Topic

This code allows you to use Win32 DLLs in your .NET applications.

This will show how to make a "hello world" console application in Visual Studio 2008 with C#. Let VS.Net do the work and create a new console application using the menu. Use Console.WriteLine and Console.ReadLine for simple input and output.

The ButtonsCS project. Create a classic "Hello, World" application using Visual Studio .Net with C# syntax. Requires either the full version or Visual C# Express Edition.

A Dictionary is a data type which maps a key to a value. The key and the value can be any type, the Dictionary shows the link between the two.

This example shows the relationship between the 3-letter airport code and their location. The code will produce a message box which says "Los Angeles."

Boxing is the conversion of a value type to the object type (or to any interface type that is implemented by the value type). Unboxing is the conversion from an object type to a value type (or from an interface type to any value type that is implemented by the value type).

C# supports abstract class members and abstract classes using the abstract modifier. An abstract class is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties. An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the abstract keyword.

In C#, you specify each class and each class member's visibility with an access modifier. The C# access modifiers are the traditional public, protected, and private plus the two additional .Net modifiers internal and protected internal.

Internal indicates members are accessible from types in the same assembly. Protected internal indicates members are accessible from types in the same assembly as well as descendant classes. OO purist might object to internal and protected internal and I suggest you choose private, protected, or public over them until you both fully understand them and have a need that is best suited by them.

The default for class and class members is Internal (members are accessible from types in the same assembly). This is different than with interfaces where the default for an interface is Internal but an interface's members are always public -- which makes sense but is noteworthy.

With both classes and interfaces, if you make a class public, the members are public. This applies to the other access modifiers too. For example, if you make a class protected, the members default access modifiers are protected.

Languages Focus: Assignment

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

General Info: Associative Array

Languages Focus: Associative Array

Associative arrays are also known as a dictionary or a hash table in other languages.

In C#, the Object keyword is an alias for the base System.Object class and is the single base class all classes ultimately inherit from.

C# is case sensitive. The following does NOT:

The first time you type any other case for commands or variables, VS.Net will change it to the accepted or defined case. For example, if you type messagebox.show it is converted to MessageBox.Show. Once corrected, you can break it again by editing MessageBox to messagebox and the compiler will give you an error.

In C#, you use the class keyword to specify a class and you signify its parent with a colon and the name of the parent class. When you instantiate an object from a class, you use the new keyword.

For C#, I prefer to put the opening { and the closing } on their own line (as opposed to C++, Java, and JavaScript where I put the opening bracket at the end of the first line.

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus: Comparison Operators

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

In C#, you define constants with the const keyword.

All constants are part of a class (no global constants) but you can make a constant public and have access to it so long as you have added the class to the project (even without creating the class as if they were static, but you cannot use the static keyword).

Constants must be of an integral type (sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, bool, or string), an enumeration, or a reference to null.

In C#, a constructor is called whenever a class or struct is created. A constructor is a method with the same name as the class with no return value and you can overload the constructor. If you do not create a constructor, C# will create an implicit constructor that initializes all member fields to their default values.

Constructors can execute at two different times. Static constructors are executed by the CLR before any objects are instantiated. Regular constructors are executed when you create an object.

Note: C# requires () in both the function declaration, and when it's invoked.

C# projects require the .Net framework and any additional dependencies you've added such as Crystal Reports.

In Visual Studio.Net, you can create a Setup and Deployment project by using any of the templates available on the New Project dialog (Other Project Types).

In addition, C# projects also support ClickOnce which brings the ease of Web deployment to Windows Forms and console applications. To get started, right click on your solution in the Solution Explorer, click Properties then select the Security tab. 

In addition, you can use any of the many free and commercially available installation packages.

Languages Focus: Development Tools

Primary development tool(s) used to develop and debug code.

The .Net framework offers a static method in the string class: String.IsNullOrEmpty.

C# uses a semicolon ";" as an end of statement specifier and you can put multiple statements on a single line of code if you wish as well as split a single statement into two or more code lines.

C# uses a try...catch...finally statement to trap for errors.

Common source code file extensions include:

• .SLN - Solution File. Contains solution specific information such as links to the projects within this solution.
• .CSPROJ - C# Project File. Contains project specific information.
• .CS - C# source file.
• .Designer.CS - C# form file (a text resource file).

Use a destructor to free unmanaged resources. A destructor is a method with the same name as the class but preceded with a tilde (as in ~ClassName). The destructor implicity creates an Object.Finalize method (you cannot directly call nor override the Object.Finalize method).

In C# you cannot explicitly destroy an object. Instead, the .Net Frameworks garbage collector (GC) takes care of destroying all objects. The GC destroys the objects only when necessary. Some situations of necessity are when memory is exhausted or you explicitly call the System.GC.Collect method. In general, you never need to call  System.GC.Collect.

Use () around evaluation with no "then".

Simple syntax example of class inheritance.

C# does not support multiple implementation inheritance. Each class can have only one parent class (a single inheritance path). In C#, you can use multiple interface usage to design in a multiple class way horizontally in a class hierarchy.

In C#, inlining is automatically done for you by the JIT compiler for all languages and in general leads to faster code for all programmers whether they are aware of inlining or not.

Classes and structs can inherit from interfaces in a manner similar to how classes can inherit a base class or struct, but a class or struct can inherit more than one interface and it inherits only the method names and signatures, because the interface itself contains no implementations.

Literals are quoted as in "Prestwood". If you need to embed a quote use a slash in front of the quote as in \". 

Same as C++ and Java. C# logical operators:

In C# you can set the visibility of a member field to any visibility: private, protected, public, internal or protected internal.

You can intialize a member field with a default when declared. If you set the member field value in your constructor, it will override the default value.

Finally, you can use the static modifier (no instance required) and readonly modifier (similar to a constant).

In C# you can set the visibility of a member field to any visibility: private, protected, public, internal or protected internal. You can intialize a member field with a default when declared. If you set the member field value in your constructor, it will override the default value. Finally, you can use the static modifier (no instance required) and readonly modifier (similar to a constant).

The method modifiers are abstract, extern, new, partial, sealed, virtual, and override. Specify C# member modifiers as follows:

abstract SomeMethod() {..}

The field modifiers are const, readonly, static, volatile. Specify field modifiers as follows:

readonly int MyAge;

In C#, parens indicate a method and the lack of parens indicate a property. You use special get and set methods to both get and set the values of properties. For a read-only property, leave out the set method. The value keyword is used to refer to the member field. Properties can make use of any of the access modifiers (private, protected, etc). It is common to use a lowercase member names for member fields ("name" in our example) and uppercase properties to manage member fields ("Name" in our example).

Commenting Code
C# uses "//" for a single line comment and /* */ for a multiple line comment.

The null-coalescing operatior ?? is used to assign a default value for nullable value types or reference types. This operator prevents exceptions from being thrown when trying to assign a nullable type to a non-nullable type.

For example, this code will throw an exception.

However, this code will assign the default value of -1 to y:

C# Overloading

• Operator - Yes.
• Method - Yes.

Method overriding allows you to define or implement a virtual method in a parent class and then replace it in a descendant class. In C#, you specify a virtual method with the virtual keyword in a parent class and replace it in a descendant class using the override keyword.

Language Overview: C# is an OOP language (no global functions or variables) and is type-safe. You code using a fully OOP approach (everything is in a class).

Target Platforms: C# is most suitable for creating any type of application that runs on the .Net platform. This includes desktop business applications using WinForms and websites using WebForms.

Defining
In C# the data type of each parameter must be specified, even if adjacent parameters are of the same type.

C# uses the keyword partial to specify a partial class. All parts must be in the same namespace.

A partial class, or partial type, is a class that can be split into two or more source code files and/or two or more locations within the same source file. Each partial class is known as a class part or just a part. Logically, partial classes do not make any difference to the compiler. The compiler puts the class together at compile time and treats the final class or type as a single entity exactly the same as if all the source code was in a single location.

You can use them for many things including to separate code generator code, organize large classes, divice a class up so you can split ownwership among multiple developers, have different versions of the same class, and to utilize multiple languages with a single class.

Although pointer data types in C# coding are less important than in other languages such as C++, C# does support developer defined pointers. Use the * operator to declare a pointer data type. Use the & operator to return the current address of a variable.

In .Net managed coding the use of pointers is not safe because the garbage collector may move memory around. To safely use pointers, use the unsafe keyword.

C++/CLI has more extensive support for pointers than C#. If you have needs that go beyond what C# offers, you can code in C++/CLI and add it to your project.

C# supports the following types of polymorphism:

• Parametric Polymorphism (Overloading)
• Inheritance-Based Polymorphism
• Interface-Based Polymorphism
• Ad-Hoc Polymorphism
  

With C#, use the sealed keyword to prevent a class from being inherited from and to prevent a method from being overridden.

A method marked sealed must override an ancestor method. If you mark a class sealed, all members are implicitly not overridable so the sealed keyword on members is not legal.

For WebForm applications the client target is the browser (a document interfaced GUI), a common solution is to simply output an HTML formatted page with black text and a white background (not much control but it does work for some situations). For WinForm applications, Crystal Reports is still a popular choice with C# developers because it has been bundled with many Microsoft products, it's overall popularity, and compatibility with many different development tools.

To refer to the current instance of a class, use the this keyword. The this keyword provides a way to refer to the specific instance in which the code is currently executing. It is particularly useful for passing information about the currently executing instance.

The this keyword is also used as a modifier of the first parameter of an extension method.

You cannot use this with static method functions because static methods do not belong to an object instance. If you try, you'll get an error.

C# supports both static members and static classes using the static keyword. You can add a static method, field, property, or event to an existing class. Also, you can designate a class as static and the compiler will ensure all members in that class are static. You can add a constructor to a static class to initialize values.

The CLR automatically loads static classes with the program or namespace.

C# String Concatenation

C# performs implicit casting of numbers to strings. To concatenate two strings, a string to an integer, or a string to a floating point number, use the + operator. For example, to convert a floating point number to a string just concatenate an empty string to the number as in "" + 3.2.

Alternatively, you can use the System.Text.StringBuilder class which frequently but not always provides faster code.

C# Substring

Above returns "abcd" on a string literal. You can, of course, use VarName.Substring(0, 4).

An operation with only one operand (a single input). The following are the C# unary operators: +, -, !, ~, ++, --, true, or false.

C++, Java, and C# all use C-like variable declaration.

C# has C-like variable declaration and although variables are case sensitive, VS.Net will auto-fix your variable names to the defined case.

C# offers many variable types. Some common types used include short, int, long, float, double, decimal, Int16, UInt16, Int32, Int64, string, and bool.

You can also specify the value when you declare a variable as in:

To restrict what an ASP.NET application can and cannot access and to provide an additional level of application isolation in a hosted environment, access security can be used. You do this by configuring the element in the machine-level Web.config file located in the following folder: %windir%\Microsoft.NET\Framework\{version}\CONFIG.

Using this quickie code snippet, you can attach an ASP:Gridview  to an external RSS Feed.

All you need to accomplish this is the URL of a usable feed.

A quick example to demonstrate the yield keyword in the .NET Framework

Add new methods to predefined types and objects with extension methods (no need to recompile the base code).  To use this extension, all i have to do is include the  namespace ExtensionExample.

Demonstrates the code required to retreive and store a file uploaded via an ASP FileUpload object.  Assumes you have a web form with a FileUpload, a button, and a label control.  Also, this example stores the file uploaded into a folder named "Uploads" which is assumed to pre-exist.

Retrieves an array of all the components of any given type within a starter control (such as a page, table, panel, etc.)  This routine is recursive and will keep iterating down until all the embedded components are found.

This C# code can be invoked to produce an array as  follows:

How do you resolve the UserID of a user when using ASP.NET 2.0's built in Membership utility?

This code shows how to ask the webserver where the site's root directory is, and how to convert a relative path (like /Uploads) to the full filesystem path.  This will work across environments (i.e. Development/QA/Production).

Variables that only contain a reference to the values. Reference data type variables only contain a reference to it's constituent value.  Reference data types include objects and strings.  Assignment of one reference type variable to another copies the reference, thus changes to the values in one variable changes the values in the other.

First, you must add the System.Net.Mail namespace to your project. There are 2 objects we use to send the email, a MailMessage, and an SMTPClient.

This code works from C# projects or from ASP.NET projects. Make sure your mail server is set to relay messages for whoever might be sending the message. In my case my webserver is sending through my exchange server so I had to tell exchange to relay for my webserver.

This article will show how to access a function in a legacy COM dll from a ASP.NET web page. By legacy I mean a dll that is not a .NET managed code dll (a Win32 DLL). 

When designing a WinForms application, the most straightforward way to authenticate a user is using NTLM or Active Directory using WindowsIdentity.GetCurrent. Over the Internet, you can use the whole ASP.Net security setup with Membership.GetUser. The GenericPrincipal object works well when you deploy to a mixed web/WinForms environment. See new GenericIdentity.

Can I use a Win32 DLL in my Visual Studio.Net application?

VB Classic supports a form of single level inheritance where you, in essence, create an abstract class and then implement it in one or more classes that inherit from the abstract class. However, you cannot have any further descendant classes so "prevent derivation" is implemented by design of this simple inheritance model.